1. Technical Field
The present invention relates to laser or infrared welding of parts and, more particularly, to a guide for conveying laser energy to a weld zone.
2. Discussion
The art of welding parts incorporates a variety of techniques including ultrasonic welding, heat welding, and, most recently, Through Transmission Infrared (TTIr) welding of plastic parts. During TTIr welding, laser radiation of a suitable wavelength is passed through a first transparent plastic part and impacts an absorbent polymer whereupon the absorbent polymer is heated to a critical melting temperature. When the absorbent polymer part begins to melt, the parts are pressed together. A weld or bond joins the parts as the melt cools.
While the area of TTIr welding has seen considerable advancement, difficulties related to the integrity and uniformity of the weld as well as controlling the transmission of the laser energy to the weld zone remain as some of the barriers to widespread commercial application of TTIr welding. In most TTIr systems a spot laser tracks the weld line either through movement of the laser or the workpiece. An alternative approach is to illuminate the entire weld zone through a coordinated alignment of laser diodes. The simultaneous illumination approach provides numerous advantages including the speed at which the weld is created and the uniformity of the resulting bond. However, simultaneous illumination of the entire weld surface requires precise alignment of the laser diodes relative to the workpiece. In weld zones consisting of linear or simple geometric configuration, the alignment of the diodes do not present a significant impediment to use of TTIr welding technology. However, for weld zones having complex two-dimensional or three-dimensional curvatures, diode alignment is a significant concern. For welds with complex curvatures the diode mounting manifolds must permit three-dimensional rotation and three-dimensional translation of the diodes for proper alignment. The configuration of the manifold will often times be different for each application and, in some instances, may be cost prohibitive.
An additional difficulty related to the configuration of the diode array is that the individual diodes within an array are generally aligned to slightly overlap one another to provide uniform energy along the weld zone. In this configuration, failure of a diode or diode element called an emitter creates an area within the weld zone that is subjected to less laser energy during welding. A weakness in the weld may result. While feedback circuits may be used to detect a failed diode and prevent the manufacture of a large number of defective parts, the failed diode should be replaced prior to further production.
The present invention focuses on a method and apparatus for directing a laser beam to a weld zone for infrared/laser welding. While the present invention may be most applicable for use in TTIr welding, it may also be used in other modes of infrared/laser welding such as surface heating. The invention permits mounting of the laser diodes in a configuration that need not directly correspond to the configuration of the weld zone. The laser energy generated by each diode is transmitted through a transparent flexible sheet of material referred to herein as a light guide. The entrance and exiting surfaces of the light guide are generally smooth to minimize diffusion and the light guide is preferably formed of a flexible material that provides total internal reflection. The light guide may be contoured such that its exit surface matches the weld contour while allowing the diodes to be mounted in a dissimilar configuration such as on a flat manifold.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.